The invention relates to a method for detecting a tow start operation of an internal combustion engine in a motor vehicle.
Under some circumstances it can occur that the internal combustion engine of a motor vehicle is not started by a vehicle's internal starter unit, but rather is tow started by hand. This is the case, for example, when the starter or an additional component of the vehicle start-up system is defective or when the available power of the starter battery, which can depend on the temperature, is too low, and, therefore, it is not possible to start the internal combustion engine. If the vehicle or rather the internal combustion engine is tow started, it can usually be assumed that (with the exception of a discharged battery) it will not be possible to re-start the internal combustion engine again until the defect in the vehicle has been remedied. If the driver turns off the internal combustion engine, or if owing to the operating conditions or additional functions, the internal combustion engine is automatically switched-off, it is possible, as a rule, to re-start again only by tow starting the internal combustion engine. In principle, however, it has not been possible to differentiate to date a tow start operation of the internal combustion engine in motor vehicles from a conventional start-up process by use of a starter or starter unit. Therefore, measures with respect to the operating mode of the internal combustion engine or specific functions that block the switching-off process of the internal combustion engine cannot be initiated.
The object of the invention is to provide a method by which it is possible to differentiate a tow start operation of the internal combustion engine from a conventional start-up process of the internal combustion engine by way of a starter unit.
This object is achieved by a method for detecting a tow start operation of an internal combustion engine in a motor vehicle, wherein a signal, representing the activity and/or inactivity of a starter unit of the internal combustion engine, is detected, and the tow start operation of the internal combustion engine is detected, when following detection of a successful start-up process of the internal combustion engine, the signal, representing the activity and/or inactivity of the starter unit, has not displayed any activity of the starter unit since the beginning of the start-up process of the internal combustion engine. Advantageous further developments are disclosed herein.
In one aspect of the invention, a tow start operation of the vehicle's internal combustion engine is detectable by the activity or inactivity of the starter, in particular, the starter unit. The inventive method for detecting a tow start operation of an internal combustion engine in a motor vehicle is characterized in that a signal, representing the activity and/or inactivity of a starter unit of the internal combustion engine, is detected and evaluated. A tow start operation of the internal combustion engine is detected, when following detection of a successful start-up process of the internal combustion engine, the signal, representing the activity and/or inactivity of the starter unit has not displayed any activity of the starter unit since the beginning of the start-up process. Therefore, the exclusive principle allows one to conclude in the absence of a starter actuation that external influences have caused the start-up process of the internal combustion engine, and, that working on this basis, an unintentional automatic shut-off process of the internal combustion engine is inhibited.
A successful start-up process of the internal combustion engine is detected advantageously when the initiation of a start-up process is detected, and when, for example, at the end of the start-up process, a speed overrun of the crankshaft speed is detected. A (successful) start-up process of the internal combustion engine, thus, a transition from the immobile engine to the running engine, can be detected by evaluating a signal that represents the activity of the internal combustion engine, for example, by evaluating the crankshaft speed. Then, a successful start-up is detected at the end of the start-up process by a speed overrun that occurs and is detectable and/or by reaching the idle speed. Such a detection of a successful start-up can be rendered plausible in its temporal sequence by an evaluation within a time frame and can be improved by additional timing and debounce mechanisms.
If the beginning of a start-up process is identified (for example, by means of the transition from the immobile to the rotating crankshaft), then the activity and/or inactivity of the starter unit of the internal combustion engine is checked by evaluating the signal, which represents the activity and/or inactivity of the starter unit of the internal combustion engine, advantageously for a predetermined time frame or speed that is predetermined for the internal combustion engine. The signal, representing the activity and/or inactivity of the starter unit, is configured advantageously in such a manner that when the activity of the starter is detected, the signal changes its status from “inactive” to “active.” The signal can be reset from the “active” status to the “inactive” status after a predetermined time interval and successful evaluation upon reaching the end of the start-up process and successful evaluation and/or as a function of the speed of the internal combustion engine or on shutting down the internal combustion engine. As the final condition for a successful tow start operation, there must also occur, in addition to the inactivity of the starter upon initiation of the start-up process, the success of the tow start operation through the detection of the termination of the start-up process—only then may the tow start operation be evaluated as having occurred.
As already stated above, on detection of a tow start operation of the internal combustion engine, a variety of measures may be initiated with respect to the operating mode of the internal combustion engine. These measures lead to an improvement in the operating mode when the internal combustion engine is tow started. On detection of a tow start operation of the internal combustion engine, predetermined vehicle functions can be deactivated advantageously, for example, for the duration of a driving cycle, thus until the next manually conducted shut-off process of the internal combustion engine. These predetermined vehicle functions could enable or rather initiate an automatic shut-off process of the internal combustion engine.
If the motor vehicle is equipped, for example, with a hybrid drive unit, consisting of an internal combustion engine and an electric motor for driving the motor vehicle, it would be logical, for example, to inhibit the drive from changing from the internal combustion engine to the electric motor (that is, an automatic stop process of the internal combustion engine), if a tow start operation of the internal combustion engine was detected, for example, owing to a defective start-up system. This measure would prevent the vehicle from coming to a standstill following a change-over of the drive from the internal combustion engine to the electric motor, because even then the start-up system cannot re-start the internal combustion engine owing to a defect in the start-up system. In that case, it would not be possible to again start-up the internal combustion engine. Hence, there exists the risk of a breakdown.
If the motor vehicle is equipped with an automatic internal combustion engine stop function, which can be part of a so-called “automatic start/stop function”, then an advantageous configuration of the invention provides that upon detection of a tow start operation of the internal combustion engine, this function is deactivated, or the implementation of its stop commands is blocked, because in the event that a tow started internal combustion engine is automatically shut-off, a re-start cannot be guaranteed as a rule. If the internal combustion engine were to be automatically shut off, it is very likely that it would have to be tow started again.
In summary it must be pointed out that upon detection of a tow started internal combustion engine, a variety of different measures can be initiated in order to avoid a so-called “stranded vehicle.” In this way, warranty costs and customer complaints can be avoided.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.